1. Field of the Invention
The present invention relates to an external battery charger, and more particularly to an external battery charger which is selectively operable for use with an extra charging battery and a battery powered electronic device, and to a method of charging the extra battery using the charge.
2. Description of the Related Art
Recently, rechargeable batteries, i.e., secondary batteries, have been widely used in battery powered electronic devices, for example, portable radio cassette players, portable computers, camcorders, cellular telephones, etc. Hitherto, alkaline batteries such as nickel cadmium (Ni--Cd) or nickel metal hydride (Ni-MH) batteries have been generally used as the secondary battery. Today, lithium ion (Li-ion) batteries of an organic electrolytic cell have gained big popularity in high-end portable electronic devices, since they exhibit high energy density, low temperature characteristics, and stable storage capability.
The abovenoted rechargeable batteries require a charger for charging the batteries. The charger includes an internal charger equipped in the battery powered device; this charger will begin charging the battery whenever the device is powered by AC power. Further, an external battery charger has been implemented; this charger has an independent power supply and connectors for accepting one or more batteries to be charged.
The external battery charger is useful for the users of battery powered devices to prepare extra charged batteries. Extra charged batteries or batteries are carried to operate the portable electronic devices for lengthy periods of time in environments where AC power is unavailable. When the external battery charger is optionally adopted in a portable computer, for example, usually an AC adapter is used to supply power to the external battery charger or alternatively to the internal battery charger of the portable computer. Thus, while the AC adapter is used with the external battery charger, the portable computer must be operated by battery power. If it is necessary for the portable computer be operated with AC power, the user must use another AC adapter which results in additional expense.
Further, if the portable computer is operated with the DC power supplied by the AC adapter, it has been found that the load current at the output of the AC adapter is considerably reduced when the portable computer has entered a power saving mode of operation.
Therefore, a need arises in the external battery charger to share the DC power supplied by an AC adapter with a portable computer and to charge extra batteries with the remainder of the power used by the portable computer.
The following each disclose features in common with the present invention but do not teach or suggest the specifically recited external battery charger of the present invention: U.S. Pat. No. 5,189,358 to Tomura et al., entitled Adaptor For Mounting Portable Radio Apparatus To Moving Body And Charger For Portable Radio Apparatus, U.S. Pat. No. 5,073,837 to Baek, entitled Low Voltage Protection Circuit, U.S. Pat. No. 5,200,685 to Sakamoto, entitled Adapter For External Battery And Batterer System, U.S. Pat. No. 5,272,382 to Heald et al., entitled Power Supply For Computer System Manager, U.S. Pat. No. 5,317,249 to Ford, entitled Transmit Mode Detector In A Battery Charger, U.S. Pat. No. 5,347,163 to Yoshimura, entitled Power Supply Backup Device For Use In Portable Electronic Apparatus, U.S. Pat. No. 5,465,039 to Narita et al., entitled Power Supply For Electronic Device, And Electronic Device System, U.S. Pat. No. 5,664,203 to Hong et al., entitled Peripheral Device Input-Initiated Resume System For Combined Hibernation System And Back-Up Power Stipplv For Computer, U.S. Pat. No. 5,661,780 to Yarnamoto et al., entitled Cordless Telephone Having Power Failure Detection Circuit, U.S. Pat. No. 5,721,481 to Narita et al., entitled Battery Charger For An Electronic Device And A Spare Battery, U.S. Pat. No. 5,610,450 to Saeki et al., entitled Power Supply Apparatus For Efficiently Utilizing Battery And Electronic Apparatus Using The Power Supply, U.S. Pat. No. 5,583,417 to Yuen, entitled Power Sharing Detector For Use With A Battery Charger And An Auxiliary Device, U.S. Pat. No. 5,572,110 to Dunstan, entitled Smart Battery Charger System, U.S. Pat. No. 5,557,738 to Townsley et al., entitled Power System Configuration And Recovery From A Power Fault Condition In A Computer System Having Multiple Power Supplies, U.S. Pat. No. 5,563,493 to Matsuda et al., entitled Power Source System Of Portable Information Processing System Using Battery, U.S. Pat. No. 5,553,294 to Nanno et al., entitled Portable Computer Powered By Rechargeable Batteries, U.S. Pat. No. 5,481,730 to Brown et al., entitled Monitoring And Control Of Power Supply Functions Using A Microcontroller, U.S. Pat. No. 5,483,464 to Song, entitled Power Saving Apparatus For Use In Peripheral Equipment of A Computer, U.S. Pat. No. 5,534,762 to Kim, entitled Self-Propelled Cleaning Robot Operable In A Cordless Mode And A Cord Mode, and U.S. Pat. No. 5,585,677 to Cheon et al., entitled Backup Power-Supply System For Emergence.